I am a little confused because up untill recently Best Buy and a few other retailers had the system requirements as low as XP.

Tried going to a Best Buy just to read the box, but they are sold out.

So I guess I can attach the Express to the powerline adapter and configure it through the Windows 7 machine?

I have the 2012 Airport Express box in front of me right now. It doesn't list the Windows requirements on the box, but it is in the manual.

To set up AirPort Express using a Windows PC, you need:

A Windows computer with a 300 MHz or higher processor and Wi-Fi certified wireless capability (to set it up wirelessly), or a Windows computer connected to the AirPort Express with an Ethernet cable (to set it up using Ethernet)

Windows 7 (SP1)

AirPort Utility for Windows v5.6.1 or later

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I see no reason why you can't attach it to the power line adapter, but I would connect it directly to the Windows 7 machine's ethernet port to avoid potential issues.

Best of luck, it's a real nice product. I just set one up in my home last week. It works much better than the 2.4GHz Linksys Cisco router I was using.

BTW if you have an (iPad, iPhone, iPod Touch) with iOS 5.0 or higher, you can also set up the Airport Express with it. Just download the Airport Utility app from the App store.

Microsoft told developers that they will support there machines for another 10 years with xp and with vista but no one else will support them with hardware kinda lame

Well, if anybody is going to support Windows for 10 years of course its going to be Microsoft.

But isn't Microsoft supporting XP reluctantly because so many have resisted upgrading?

At some point Apple has to let an older operating system go (especially one that is not thier own) because trying to get newer tech to work with older operating systems is probably a waste of resorces.

Of course Apple is gearing up for Windows 8 so they probably decided having Vista support also is too big a range to deal with.

That being said I have to give Apple credit. My 2nd gen Airport Extreme works better with my windows machine the routers I have had by belkin, linksys and D-Link, routers made to work specifically with Windows.

Its this fact that made me take Apple pretty serioulsy. Though I have not made the complete switch yet, I plan on it in the future.